Tantalum (Ta) thin films are widely used in manufacturing of semiconductor and micro-electromechanical (MEM) devices. For example, in semiconductor integrated circuit manufacturing, tantalum may be used as a diffusion barrier between copper and silicon. Tantalum may also be used as a gate electrode in metal oxide semiconductor field effect transistor (MOSFET) devices. Tantalum may also be used to absorb X-rays in X-ray masks. In thermal inkjet MEM devices such as a printhead, tantalum is used as a protective overcoat on the resistor and other substrate layers to protect the underlying layers from damage caused by cavitation from the collapsing ink bubbles.
Beta-tantalum is typically used in the manufacture of thermal inkjet devices, because it has not been possible to stabilize the alpha-tantalum phase in the compressive state of stress. The tantalum layer is traditionally composed of the metastable tetragonal phase of tantalum, known as the beta-phase or “beta-tantalum.” Beta tantalum initiates during growth because of: 1) the presence of gas impurities present in the growth chamber, and 2) the underlying material type on the substrate. This conventional, default beta-tantalum layer is brittle and becomes unstable as temperatures increase. Above 300° C., beta-tantalum converts to the body-centered-cubic (bcc) alpha-phase or “alpha-tantalum.” The thermo-mechanical conditions imposed during the firing of the ink, drive the default metastable beta-tantalum to convert to alpha-tantalum. Alpha-tantalum is the bulk equilibrium or the stable-phase of tantalum. It is essential to form compressive films on thermal inkjet printheads and other fluid ejection devices because films under tensile stress would peel off the substrate, blister or delaminate, thus limiting the useful life of the printhead.
For these and other reasons, there exists a need in the art for the present invention.